Why? People are much more biased than machines. If this algorithm is well written and unbiased then we may have a case of someone saving books that speak to their biases. What if it was revealed it was books about young earth, anti-vaccination, promotion of Islamic extremism, and white supremacy? Would you be so welcoming of these rebel librarians?
The nice part of the algorithm is that, in theory, it should just be looking at circulation numbers and culling appropriately. Regardless, this is all a stop-gap measure until we can get every library digital so we don't have to worry about shelf space.